The road beckons to Tori Amos, then beckons some more. While she has a reputation for being one of the new "sensitive girl" rockers, she's a hardy "road dog" too, by her own admission. She says she has played 2,200 shows since 1991, which averages out to 244 per year.

"You don't get a loyal fan base just with hits. You get it by going from town to town like the old vaudeville acts," says Amos. "Like the troubadours, you go from village to village, castle to castle. You've got to do it.

"Look at Bruce Springsteen. He's a road dog. He put the time in. And there's something to be said for that," Amos adds. "If you don't go to these towns and sweat, if you don't trip and fall and give that to people and make yourself vulnerable and also metamorphize with them, then you don't have that relationship with them. You just don't. End of story."

Amos's latest incarnation is with Alanis Morissette. The two share double billing on a tour that comes to the Tweeter Center on Tuesday. They have distinct musical styles yet have been quite supportive of each other, says Amos, who credits Morissette with first suggesting the tour.

"We get along very well," says Amos. "It's like two pirate ships that have gone into the same cover together."

The two women have offered to share chefs, a masseuse, and, on each show night, some time together before performing. The only thing they don't do is sing onstage together.

"No, it's not the Christian campfire-girl thing, where we roast marshmallows and sing 'Kumbaya,"' says Amos. "We're two separate people, but we're orbiting together. We see each other before the show always and we talk. ... We talk about what happened with our day. She was water-skiing yesterday, and I was with my niece who was telling me family stories. Each day we touch base, and it's not a studied thing. It's just hanging out, and you have to trust that is going to set a tone."

Amos, who will release the double-album "To Venus and Back" on Sept. 21 (one disc is live, the other is a studio disc), describes herself as a "lone wolverine," so she was flattered to receive Morissette's invitation to share a tour. (Morissette was unavailable for an interview this time.) "Because it came from her, it meant something to me," says Amos. "And I don't feel a sense of division with her. I also like to watch her show from the wings. I just sense that this is an event. It's about two individual shows going on with two crews. To me, it's like a Dionysian ceremony with two storytellers."

Although it's advertised as a double bill, Amos opens for Morissette each night. They each play for 75 minutes. Amos has no ego problems with this order, and even rejected Morissette's suggestion that the two flip-flop every night, as many stars do in double-bill situations.

"I said to her, 'Are we both confident enough that your audience will come early and stay, and that mine won't leave early?' We knew we had to have the courage to do this, and it's working," says Amos. "It's kind of like Torville and Dean."

Amos has been so busy with this tour and her other touring dates and recording plans that she hasn't had time to do much else.

"I get calls like, 'Do you want to write with so and so' or 'Do you want to work with so and so.' Moby called me and I would have loved to have worked with him on his new record. But I was just walking into the studio at the time realizing that I was going to be recording my own new album. The timing wasn't great. So, there are outside things that you wish you could do, but you can get seduced into trying to do too much."

The studio portion of "To Venus and Back" turned out beautifully. Amos first thought she might just do a couple of new numbers to go alongside some B-sides, but the muse struck and she kept going.

So how was the Venus metaphor conceived? "I was talking with my girlfriends," she notes. "I said I need to go somewhere and come back from somewhere [on this record]. They started mentioning places and I said, 'Oh, no, I'd never go there.' And then one of them, Natalie, looked at me and said, 'You know, you would go to Venus if you could.' She giggled and said, 'I think that's where you try to go when you play.' And that's how it began, really."

The "Venus" studio disc was made with the band that has been touring with her for the past couple of years. It's filled with Amos's provocative lyrical imagery (the song "Juarez" addresses the unsolved murders of many women in the desert where "no angel came"). It also has some of the best vocals of her career, embedded in modern, special-effects-laden soundscapes that move from electronica-spiced piano pop and hip-hop to ambient space music.

"Well, you can't call your record 'Venus' and not be modern, right?" she says with a laugh. "You can't go retro with a name like that."

Other new songs of note (she may slip only one or two into Tuesday's show because the album isn't out yet) include the atmospheric "Suede," the spiraling "Concertina," the airy "Lust," the alluring "Spring Haze," and the show-stopping "Glory of the '80s." The latter recalls her days in Los Angeles (where she moved after growing up in the Washington/Baltimore area) and the "silicon party Barbies," a "space cake high," and "auditioning for reptiles" in the entertainment industry. In short, it's vintage Tori.

For now, however, it's back to the road and the touring circuit. "I do it because I love it," she says. "And, you know, I'd still be humming something in my head, even if I didn't do it out loud."